The present invention relates to ambient noise-reduction systems for communications apparatus such as cellular phone handsets, walkie-talkies or the like, and it relates more especially to systems for handsets that are capable of being used both with and without listening devices such as earphones, headphones or headsets. That is, the user of the apparatus may choose, at any given time, to listen directly to the internal loudspeaker provided in the apparatus, or to listen using a wired or wireless listening device connected temporarily to the handset.
It has been proposed to provide ambient noise reduction in a cellular phone handset, by providing a signal processing device that receives a signal derived from detected ambient noise, and generates a sound that tends to cancel the effect of the ambient noise at the ear of the user.
It has now been recognized that, if ambient noise reduction is to be provided in a communications apparatus that can be listed to either directly by means of an internal loudspeaker or by means of a separate listening device, the ambient noise reduction must take account of the fact that the use of the separate listening device changes the sound environment, in terms both of the degree of exposure to ambient noise and of the noise-sensing and signal-processing approaches needed to reduce the ambient noise as perceived by the user.